This invention relates to a semiconductor device, particularly a monolithic semiconductor device including a driving transistor and an output transistor in the Darlington connection, and also to a method of manufacturing the semiconductor device and an application thereof.
In a case where a power transistor which includes a driving transistor and an output transistor in the Darlington connection is employed as an element for switching the current of an inductive load in, for example, an electronic ignition device of an automobile, a very great surge voltage is sometimes generated from the inductive load. When the surge voltage exceeds the breakdown voltage of the power transistor, the power transistor is destroyed in some cases.
By connecting a Zener diode between the base and collector or emitter of the power transistor, it is possible to prevent the power transistor from being destroyed due to the surge.
However, with a construction in which the Zener diode is connected outside the finished power transistor, the number of external components of the electronic device increases, and also the number of man-hours for assemblage increases.
The Zener diode for the above-described use must be selected so as to have a Zener voltage which is higher than the operating voltage of the power transistor to be protected and which is lower than the breakdown voltage of the power transistor to be protected. Therefore, it is subject to limitations in use.
It is more desirable that the Zener diode be formed integrally with the transistor to be protected.